The present invention relates to compounds that are useful as catalysts or catalyst components. More particularly, the present invention relates to such compounds comprising two aluminum and one Group 4 metal atoms that are particularly adapted for use in the coordination polymerization of unsaturated compounds. Such compounds are particularly advantageous for use in a polymerization process wherein at least one polymerizable monomer is combined under polymerization conditions with a catalyst or catalyst composition to form a polymeric product. In addition, the complexes of the current invention are especially useful in the production of steroregular polymers derived from .alpha.-olefins, especially isotactic polypropylene.
It is previously known in the art to activate Ziegler-Natta polymerization catalysts, particularly such catalysts comprising Group 3-10 metal complexes containing delocalized .pi.-bonded ligand groups, by using Lewis acids to form catalytically active derivatives of such Group 3-10 metal complexes. Examples of suitable Lewis acids include tris(perfluorophenyl)borane and tris(perfluorobiphenyl)borane. Examples of such processes are disclosed in U.S. Pat. No. 5,721,185 and J. Am. Chem. Soc., 118, 12451-12452 (1996), and elsewhere.
According to J. Chem. Soc. Chem. Commun., 1999, 115-116, certain specifically substituted bis-Cp zirconocenedimethyl complexes may be converted to a dicationic derivative at -60.degree. C. using multiple equivalents of trispentafluorophenylborane. The resulting metallocenes required the presence of either pendant phosphine moieties or benzyl groups on the cyclopentadienyl ring system and two equivalents of the methyltris(pentafluorophenyl)borate anion for charge balance. Upon heating even to -40.degree. C. the product decomposed to give the corresponding monocationic complex and free tris(pentafluorophenyl)borane. Finally, in Organometallics, 1998,17, 5908-5912, the reaction of the strongly Lewis acidic compound, tris(pentafluorophenyl)aluminum, with bis(cyclopentadienyl)zirconium dimethyl was shown to form an unstable (.mu.-methyl) derivative via methide abstraction, which rapidly collapsed through a back exchange reaction at temperatures above 0.degree. C. to form bis(cyclopentadienyl)methylpentafluorophenyl zirconium.
All of the foregoing attempts have failed to prepare a bis(.mu.-substituted) derivative of a metal complex that is stable at temperatures greater than 0.degree. C. for a time sufficiently long for such compound to be useful in catalytic applications, especially in the polymerization of one or more ethylenically unsaturated monomers under addition polymerization conditions. Moreover, there is no known successful preparation of bis(.mu.-substituted)aluminum derivatives of a metal complex under any circumstances.